[ntp:questions] Query about NTP accuracy

David Mills mills at udel.edu
Fri May 22 03:32:08 UTC 2009


The flip answer is see Chapter 6 in my book. The useful answer is 
accuracy doesn't degrade that much, but reliability and diversity 
actually are actually enhanced. You're better off with a carefully 
watched core of primary servers, each located in a different regional 
center and a cloud of secondary servers at strategic sites around the 
country and a cloud of department servers at each site. That's the 
design I recommended for several large companies such as BCBXA, GTE, 
Bellcore and Merrill Lynch.


Andy Yates wrote:

>Does anybody have any figures that shows the effect on accuracy of an
>NTP v3 client using a stratum 1 server rather than a stratum 2 or 3
>server? It's all in a GE LAN based scenario, commercial stratum 1
>servers connected to GPS and stratum 2 and 3 servers are typically
>dedicated Linux boxes.
>The reasons is that I would rather scale by adding strata - its a very
>big data center with thousands of clients and has several "zones" that
>are isolated. However some opinion is suggesting we run IRIG-B between
>the GPS receiver and a bunch of stratum 1 servers and clients access
>these directly. Much more expensive and any increase in accuracy from a
>client experience may be negligible.
>However I'm been pressed to supply an SLA for accuracy. My argument is
>that although you can get your stratum one server to synchronize to
>microseconds of UTP, as soon as the client uses NTP v3 over the LAN,
>even a GE LAN, then the accuracy degrades and putting well designed well
>specified stratum between the boxes is not going to decrease accuracy
>sufficiently to warrant purchasing many stratum one appliances.
>questions mailing list
>questions at lists.ntp.org

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